Frame assembly for a bicycle

ABSTRACT

A frame assembly for a bicycle having a front wheel and a rear wheel. The frame assembly preferably includes a main frame and a sub-frame, which is movable relative to the main frame and configured to carry the rear wheel. A shock absorber extends between and is connected to the main frame and the sub-frame. The main frame includes a down tube and a monolithic bottom bracket support. The monolithic bottom bracket support is connected to a rearward end of the down tube and preferably includes an opening configured to support a pedal crank assembly for rotation about a crank axis. Preferably, the shock absorber is connected to the main frame for rotation about a pivot axis positioned forward of the opening of the bottom bracket support. Desirably, the shock absorber pivot axis is positioned forward of a line passing through the crank axis and a center point of the down tube at the junction of the down tube and the head tube. In one arrangement, the monolithic bottom bracket support surrounds a portion of the shock absorber.

RELATED APPLICATION

This application is a continuation of copending U.S. patent applicationSer. No. 10/459,398, filed Jun. 11, 2003.

INCORPORATION BY REFERENCE

U.S. patent application Ser. No. 10/459,398, filed Jun. 11, 2003, ishereby incorporated by reference herein in its entirety and made a partof this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a bicycle frame. Moreparticularly, the present invention relates to a bottom bracket supportof a bicycle frame.

2. Description of the Related Art

Bicycles with frames fabricated from oversized aluminum tubing havebecome increasingly popular. Unlike steel, aluminum cannot be brazed, sothat joints between the tubes of most aluminum bicycle frames have to bewelded. A critical joint in the manufacture of modern bicycle frames isthe joint between the head tube, the top tube, and the down tube. Thefork acts as a long lever arm and can exert significant amounts ofstress on the head tube. The arrival of suspension bikes in the marketplace with stiff long-travel suspension forks has made the design ofthis junction even more critical.

Top tubes and down tubes have been getting bigger to achieve greaterstrength and rigidity. This has created problems in trying toaccommodate the larger top and down tubes. Commonly, the top and downtubes are down sized at the head tube end to mate with a standard sizedhead tube. However, this reduces the effectiveness of the oversizedtubing use for the top tube and down tube. An alternative approach hasbeen to increase the diameter of the head tubes and the associated steertube bore. While the larger diameter head tube avoids the need to crimpthe top and down tube, the approach requires nonstandard bearings andcan require a nonstandard steer tube. Significantly, this approach canadd undesired weight, which is directly contrary to the desires of themarket. Typically, manufacturers have accommodated these larger top anddown tubes by crimping the tubes at their juncture with the head tube.This obviously creates strength and repeatability issues at thejuncture.

The bicycle frames with oversized down tubes and top tubes aretraditionally constructed such that one of the top tube and down tube ismitered to the head tube only, and the other of the top tube and downtube is mitered to both the head tube and the down tube. This method ofmanufacture makes it more difficult to use complex cross sectional frametubing. Further more, having to crimp down the end of the top and downtubes and then having to perform these complex cuts makes the situationeven more difficult. This type of cutting process needs either expensiveequipment if the cutting process is automated or skillful operators ifthe cutting process is done manually.

Another important joint in the bicycle frame is between the down tubeand the bottom bracket shell. In addition to supporting a pedal crankassembly, the bottom bracket shell is often used to connect a down tubeof the main frame to a seat tube of the main frame. If the bottombracket shell is a cylindrical tube, as is common, the surface areaavailable to receive and support the seat tube and down tube is limited.As a result, the diameters of the seat tube and down tube may be limitedby the size of the bottom bracket shell, which generally is sized toreceive an industry-standard bottom bracket assembly. As noted above,larger down tubes are desirable to improve strength and rigidity of thebicycle frame.

SUMMARY OF THE INVENTION

Therefore, there is a need for a tube support, such as a head tube orbottom bracket support that will accommodate oversized tubing whilemaintaining a light weight. In addition, a preferred bottom bracketsupport defines one or more pivot axes between the main frame and thesub-frame and may also support one end of the shock absorber. Apreferred bottom bracket support permits an axis of the down tube to beoffset from a crank axis of the bicycle frame.

A preferred embodiment is a bicycle including a front wheel, a rearwheel and a frame assembly. The frame assembly includes a main frame anda sub-frame, which is movable relative to the main frame and configuredto carry the rear wheel. A shock absorber extends between and isconnected to the main frame and the sub-frame. The main frame includes adown tube and a monolithic bottom bracket support. The monolithic bottombracket support is connected to a rearward end of the down tube andincludes an opening configured to support a pedal crank assembly. Themonolithic bottom bracket support surrounds a portion of the shockabsorber.

A preferred embodiment is a bicycle including a front wheel, a rearwheel and a frame assembly. The frame assembly includes a main frame anda sub-frame, which is movable relative to the main frame and configuredto carry the rear wheel. The main frame includes a forged bottom bracketsupport, which defines an opening configured to support a pedal crankassembly for rotation about a crank axis. The main frame also includes adown tube having a substantially linear intermediate section defining adown tube axis, wherein the down tube axis extends below the crank axis.A shock absorber is connected to and extends between the main frame andthe sub-frame. The shock absorber is connected to the main frame forrotation about a pivot axis positioned forward of the opening of thebottom bracket support.

A preferred embodiment is a bicycle including a front wheel, a rearwheel and a frame assembly. The frame assembly includes a main frame anda sub-frame, which is movable relative to the main frame and configuredto carry the rear wheel. The main frame includes a head tube, a downtube and a forged bottom bracket support, which defines an openingconfigured to support a pedal crank assembly for rotation about a crankaxis. The down tube is connected to and extends between the head tubeand the bottom bracket support. A shock absorber is connected to themain frame at a first location for rotation about a first pivot axis andconnected to the sub-frame at a second location. The first pivot axis ispositioned forward of a line passing through the crank axis and a centerpoint of the down tube at the junction of the down tube and the headtube.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention are described below with reference to drawings of preferredembodiments, that are intended to illustrate, but not to limit, thepresent invention. The drawings contain five figures.

FIG. 1 is a side elevational view of an off-road bicycle, or mountainbike, incorporating a bicycle frame having certain features, aspects andadvantages of the present invention.

FIG. 2 is a side elevational view of the bicycle frame of FIG. 1 withcertain components of the bicycle removed for the purpose of clarity.

FIG. 3 is a perspective view of a head tube having certain features,aspects and advantages of the present invention.

FIG. 4 is a front view of the head tube of FIG. 3.

FIG. 5 is a cross-sectional view of the head tube of FIG. 3, taken alongthe line 5-5 of FIG. 4. A front suspension fork assembly, handlebarassembly and a steer tube of the bicycle are shown in phantom.

FIG. 6 is a top view of the head tube of FIG. 3.

FIG. 7 is an elevational view of a right side of the head tube of FIG.3.

FIG. 8 is a rear view of the head tube of FIG. 3.

FIGS. 9A-9C are cross-sectional views of the head tube of FIG. 3. FIG.9A is a cross-sectional view of an upper portion of the head tube, takenalong line 9A-9A of FIG. 4. FIG. 9B is a cross-sectional view of amiddle portion of the head tube, taken along line 9B-9B of FIG. 4. FIG.9C is a cross-sectional view of a lower portion of the head tube, takenalong line 9C-9C of FIG. 4.

FIG. 10 is a flow chart of a manufacturing method for producing the headtube of FIG. 3.

FIG. 11 is a perspective view of a forging blank used to produce thehead tube of FIG. 3.

FIG. 12 is a perspective view of a work piece formed from the forgingblank of FIG. 11 by a forging process.

FIG. 13 is a perspective view of the completed forged head tube formedfrom the work piece of FIG. 12.

FIG. 14 is a flow chart of a manufacturing method for producing ajunction between the head tube and the top and down tubes.

FIG. 15 is a partial, side elevational view of a head tube junctionproduced by the method of FIG. 14.

FIG. 16 is a cross-sectional view of the head tube junction of FIG. 15,taken along a vertical, central plane of the bicycle.

FIG. 17 is a partial cross-sectional view of the head tube junction ofFIG. 15 taken along the line 17-17 of FIG. 15.

FIGS. 18A-18C are cross-sectional views of the head tube junction ofFIG. 15. FIG. 18A is a cross-sectional view of an upper portion of thejunction, taken along line 18A-18A of FIG. 15. FIG. 18B is across-sectional view of a middle portion of the head tube, taken alongline 18B-18B of FIG. 15. FIG. 18C is a cross-sectional view of a lowerportion of the head tube, taken along line 18C-18C of FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred head tube and bottom bracket support is described inconnection with a preferred embodiment of an off-road bicycle. First, apreferred embodiment of a bicycle, including a preferred bottom bracketsupport, is described, after which a preferred embodiment of a head tubeis described in detail. Although the head tube described herein ispreferred for use in connection with an off-road bicycle as describedherein, one of skill in the art will appreciate that embodiments of thehead tube may be used in other suitable environments as well.

A. Overview of the Bicycle

FIG. 1 illustrates an off-road bicycle, or mountain bike 10. The bicycle10 is described herein with reference to a coordinate system wherein alongitudinal axis extends from a forward end to a rearward end of thebicycle 10. A vertical, central plane generally bisects the bicycle 10and contains the longitudinal axis. A lateral axis extends normal to thelongitudinal axis and lies within a horizontal plane. In addition,relative heights are generally expressed as elevations from a horizontalsurface S upon which the bicycle 10 is supported in an upright position.Similarly, relative forward and rearward positions are expressed asdistances from a vertical axis that is normal to the horizontal surfaceS. In several figures, an arrow F indicates a direction of forwardmovement of the bicycle 10. The above-described coordinate system isprovided for the convenience of describing the illustrated embodiment,and is not intended to limit the scope of the present invention.

The bicycle 10 includes a frame assembly 12 comprised of a main frame 14and an articulating frame, or sub-frame 16, pivotally supported relativeto the main frame 14. The bicycle 10 also includes a front wheel 18carried by a front suspension assembly, or suspension fork 20. A steerertube (not shown) is journaled for rotation about a steering axis A_(S)defined by the main frame 14. A handlebar assembly 22 is connected to anupper end of the suspension fork 20 and is operable to permit a rider ofthe bicycle 10 to rotate the front wheel 18 about the steering axisA_(S).

A rear wheel 24 of the bicycle 10 is carried by the subframe 16. A shockabsorber 26 is pivotally connected to both the main frame 14 and thesubframe 16 to provide resistance to articulating motion of the subframe16 relative to the main frame 14 and, thus, provide resistance to thesuspension travel of the rear wheel 24. A seat assembly 28 is supportedabove the bicycle frame 12 at a position behind the handlebar assembly22 and provides support for a rider of the bicycle 10.

A pedal crank assembly 32 is rotatably supported by the bicycle frame 12and drives a multi-speed chain drive arrangement 34. The multi-speedchain drive arrangement 34 preferably includes a plurality of sprockets,or chain rings 36, rotatably connected to the pedal crank 32. Typically,three chain rings 36 of varying size are mounted to the pedal crank 32.The chain drive arrangement 34 also includes a plurality of sprockets,or cogs 38, drivingly coupled to the rear wheel 24. A drive chain 40drivingly interconnects a selected chain ring 36 with a selected cog 38to transfer torque from the pedal crank assembly 32 to the rear wheel24. Preferably, front and rear derailleurs 42, 44 are supported by thebicycle frame 12 and are configured to move the drive chain 40 to aselected one of the chain rings 36 and rear cogs 38, respectively.

The bicycle 10 also includes front and rear brake systems 46, 48 forslowing and stopping the bicycle 10. Although the illustrated brakes 46,48 are disc-type brakes, other suitable brake systems may also be used,such as rim-type brakes for example. Rider controls (not shown) aretypically provided on the handlebar assembly 22 and are operable tocontrol shifting of the front and rear derailleurs 42, 44 and the frontand rear brake systems 46, 48.

With reference to FIG. 2, the bicycle frame 12 and rear shock absorber26 are illustrated with the remaining components of the bicycle 10removed for clarity. As described above, preferably, the bicycle frame12 is primarily comprised of a main frame 14 and an articulating frame,or subframe 16. The main frame 14 includes a head tube 50 which definesthe steering axis A_(s) of the bicycle frame 12. Desirably, the steeringaxis A_(s) is canted rearwardly from a vertical axis. The head tube 50is configured to rotatably support the front suspension 20 and, thus,the front wheel 18 of the bicycle 10.

A top tube 52 and a down tube 54 extend in a rearward direction from thehead tube 50 and diverge from one another when moving toward theirrearward ends. A bottom bracket support 56 extends between the rearwardends of the top tube 52 and the down tube 54 and together therewithdefines a generally triangular shape. The bottom bracket support 56includes a bottom bracket shell 58, which supports the pedal crankassembly 32 (FIG. 1) for rotation about a crank axis A_(c).

A seat tube 60 extends in an upward direction from a rearward end of thetop tube 52 and, preferably, is canted rearwardly from a vertical axis.The seat tube 60 supports the seat assembly 28 shown in FIG. 1.Desirably, a gusset 62 extends from a forward side of the seat tube 60to an upper side of the top tube 52 to provide additional strength tothe seat tube 60.

Preferably, the main frame 14 is constructed of individual components,as described above, which are fabricated from a metal material, such asaluminum or steel, and welded together. Desirably, the bottom bracketsupport 56 is created from a metal material by a forging process and,thus, benefits from the strength and durability advantages thatinherently result from the forging process. Preferably, the articulatingframe 16 and the shock absorber 26 are directly supported by the bottombracket support 56.

However, in alternative embodiment, the main frame 14 may be constructedin a more conventional fashion wherein the forged bottom bracket supportmember 56 is omitted and the articulating frame 16 and shock absorber 26may be pivotally connected to the welded-up tubes comprising the mainframe 14. Further, other suitable constructions of the main frame 14,including non-triangular constructions, may also be used, such as amonocoque construction, for example. In addition, alternative materialssuch as composites may also be used in whole or in part to construct themain frame 14 and/or articulating frame 16, as will readily beappreciated by one of skill in the art. The illustrated embodiment ispreferred, however, for at least the reasons discussed herein.

As described above, the illustrated bicycle frame 10 includes a shockabsorber 26 operably positioned between the main frame 14 and thesubframe 16. Desirably, the shock absorber 26 is configured to provideboth a spring force and a damping force in response to relative movementbetween the subframe 16 and the main frame 14, as is known in the art.The spring force is related to the relative position between thesubframe 16 and the main frame 14 while the damping force is related tothe relative speed of movement between the subframe 16 and the mainframe 14.

Although the illustrated shock absorber 26 incorporates a coil typespring 64, other suitable suspension springs, such as air springs, forexample, may also be used. Preferably, the damping system comprises apiston movable within a fluid cylinder of the shock absorber 26.Desirably, the piston forces hydraulic fluid within the fluid chamberthrough one or more restrictive flow paths to generate a damping forcewhen the shock absorber 26 is both extending and compressing, as isknown in the art. In addition, other types of damping arrangements, suchas inertia activated and position sensitive arrangements, may also beused, as well be readily understood by one of skilled in the art.

As described above, the subframe 16 is configured to support the rearwheel 24 (FIG. 1) for a movement throughout a suspension travel pathrelative to the main frame 14 from a relaxed position, substantially asillustrated in FIG. 2, to a compressed position, wherein the subframe 16is pivoted in an upward direction relative to the main frame 14.Preferably, the subframe 16 is a multiple linkage assembly. That is,preferably, the subframe 16 includes a plurality of linkage memberspivotally interconnected with one another. However, in alternativearrangements, a single link member may carry the rear wheel 24 formovement in a simple, arcuate suspension travel path relative to themain frame 14.

B. Detailed Description of the Head Tube

The head tube 50 is described in greater detail with reference to FIGS.3-9. The head tube 50 rotatably secures the steer tube 66 (illustratedin phantom in FIG. 5) within an opening 70 of the head tube 50. Theopening 70 extends lengthwise through the head tube 50 and, preferably,defines the steering axis A_(S).

As illustrated in FIG. 4, from a front view the head tube 50 preferablyhas a generally hourglass outer shape. With reference to FIG. 5, a lowerreinforced wall portion 72 of the head tube 50 preferably is disposed ata lower end head tube 50, nearest the front suspension fork assembly 20,and an upper reinforced wall portion 74 preferably is disposed at anupper end of the head tube 50, near the handle bar assembly 22. Asillustrated in FIG. 5, the steer tube 66 interconnects the handlebarassembly 22 and the front suspension fork assembly 20. A head setassembly includes upper and lower bearings 67, 68 (shown schematicallyin FIG. 5), which support the steer tube 66 relative to the head tube50. Preferably, the head set assembly includes upper and lower headset“cups”, which are press fit into the head tube 50 and define bearingsurfaces, or races, for the bearings 67, 68. The reinforced portions 72,74 reinforce and provide additional support for standard size bearingraces (not shown) of the headset assembly (not shown).

The reinforced portions 72, 74 each desirably comprise an annular ringat an end of the head tube 50. These annular ring portions 72, 74desirably have a thickness greater than the average wall thickness of amiddle portion 76 of the head tube. Furthermore, the lower reinforcedwall portion 72 is desirably thicker than the upper reinforced wallportion 74 because the lower portion 72 is subjected to more force thanthe upper portion 72. The force acting on the lower portion 74originates primarily from the front fork 22 (due to impact forcesapplied to the front wheel 18), which has a relatively long moment arm(measured from the front wheel 18 to the lower bearing 68). In contrast,the upper reinforced portion is subjected primarily to force originatingfrom the handle bar assembly 22, which has a relatively smaller momentarm (measured from the handlebar assembly 22 to the upper bearing 67).

To reduce the weight of the reinforced head tube 50, the head tubepreferably has a lower wall thickness in areas that experience lessstress under normal operating circumstances. A head tube reinforcedwithout consideration of non-critical and critical stress areas wouldhave considerably more mass, and weigh considerably more, than theillustrated head tube 50 made from the same material.

The head tube 50 is subjected to very strong forces acting generally inthe fore and aft directions. As described above, the fork 22 acts as along lever arm on the head tube 50 and amplifies forces experienced bythe front wheel 18. Over time, the lower end (the area generallyanalogous to the reinforced portion 72) of a conventional head tube mayovalize as a result of being subjected to cyclic fore and aft forces. Toovalize in terms of head tube technology means to deform from a roundgeometry to an oblong geometry due to forces subjected in a singleplane. Thus, in the present situation a conventional head tube tends toovalize such an opening of the lower portion of the head tube becomesoblong, with the longer axis extending in a fore-aft direction, or alongthe length of the bicycle 10. The reinforced portions 72, 74 addstrength to resist the damaging effects of the described planar forces,which are amplified by the moment arm of the fork 20 and wheel 18combination.

Preferably, the front portion 78 of the head tube 50 is not symmetricalto the back portion 82 of the head tube, in order to save weight byeliminating material in lower stress areas of the head tube 50. The backportion 82 of the head tube 50 is supported by the top tube 52 and thedown tube 54 (FIG. 2, shown in phantom in FIG. 5) and, therefore,requires less wall structure to resist ovalization. The partialcross-sectional view in FIG. 5 illustrates that the thickness of theback portion 86 of the reinforced portion 72 preferably is smaller thanthe thickness of the front portion 84 of the reinforced portion 72,because it is supported by the frame structure that it is connectedwith. Providing the back portion 86 with the same thickness as desirablein the front portion 84 would add unnecessary weight.

Therefore, the illustrated head tube 50 preferably is not symmetricallydesigned, about a lateral axis passing through the steering axis A_(S),because the head tube 50 is reinforced in critical areas and remainslight in weight with thinner wall thickness in less critical areas,taking into account the reinforcement provided by the remainder of theframe 12 (e.g., the top tube 52 and down tube 54).

Further weight savings are possible by configuring the middle portion 76of the head tube 50 such that an outer surface thereof forms adepression between the two reinforced areas 72 and 74. The front middleportion of the head tube is subjected to little stress when compared tothe upper and lower reinforced portions 72, 74. Desirably, the wallthickness of the head tube 50 in this area is reduced, which results ina main outer annular surface between the upper and lower reinforcingportions, 74 and 72, being recessed relative the front portion of theupper and lower reinforcing portions 74 and 72.

It would be simpler to manufacture a head tube that was symmetricalfront to back, but doing so would add mass and weight, or in thealternative, would result in a weaker head tube 50 susceptible toovalization if weight is reduced all around.

With reference to FIGS. 3, 4, 6, 7 and 9A-9C, preferably, a pair ofextensions, or flanges 75, extend in a lateral direction fromapproximately a midpoint of the head tube 50. Preferably, the flanges 75extend substantially the entire length of the head tube 50. Desirably,the back side 82 of the head tube 50, including a back side surface ofthe flanges 75 and the main body of the head tube 50, forms a continuouscurved surface 90 for receiving the attachment of the top tube 52 anddown tube 54 of the main frame 14. The continuous curved surface 90preferably has a constant radius 92 from a center point 94, whichpreferably is offset from the central axis of the opening 70 (thesteering axis As). As described above, such a construction permits theopening 70 to be a standard size and permits the surface 90 to have alarger, and preferably substantially constant, radius, whilesimultaneously keeping the lengthwise dimension of the head tube 50relatively small and keeping the overall weight of the head tube 50relatively low. Furthermore, the strength-to-weight ratio of the headtube 50 is increased over conventional head tubes.

Desirably, the radius 92 is proportional in size to the widest dimensionof the top tube 52 and down tube 54. The radius 92 preferably is largerthan one half the widest dimension of the top tube 52 and down tube 54to provide ample weld surface 96 on which to create a joint between thehead tube 50, the top tube 52 and down tube 54. Desirably, the radius 92is at least about 1 inch. More desirably, the radius 92 is at leastabout 1.25 inches and, preferably, at least about 1.375 inches.

In FIG. 6, the radius 92 is shown defining a circle in dashed lines.This circle represents the size a convention head tube would have to beto provide the same weld surface area of the present embodiment.However, the preferred head tube 50 disclosed herein provides acomparable weld surface, but with a much lower weight and possessing theability to utilize standard sized bearings 67, 68, which support a steertube 66 typically having a diameter of between about 1 and 1.5 inches,without the need for an adapter assembly. In order to accommodate a toptube 52 and a down tube 54 of a typical size utilized for off-road, ormountain bike, frame assemblies, desirably the radius 92 is betweenabout 1 and 2 inches. More desirably, the radius 92 is between about1.125 and 1.75 inches and, preferably, between about 1.25 and 1.5inches. However, a head tube may be produced having a radius 92 withother values for other applications, or for use in connection with otherframe constructions.

As described above, the illustrated head tube 50 provides a desirablelevel of strength at a relatively low weight. Desirably, a head tube 50intended for use in a mountain bike frame assembly 12 weighs less thanabout 200 grams. More desirably, such a head tube 50 weighs less thanabout 170 grams and, preferably, weighs less than about 140 grams.

The continuous curve of the weld surface 96 allows the top tube 52 anddown tube 54 to be cut, or mitered, with a simple circular cut, thatwill provide an efficient matching surface on the top tube 52 and bottomtube 54 for attaching to the head tube 50. Desirably, the circular cutin the top tube 52 or down tube 54 has a radius within about 0.01 inchesof the radius 92 of the weld surface 96 of the head tube 50. Moredesirably, the radius of the circular cut in the top tube 52 or downtube 54 has a radius that is the same as the radius 92.

By providing a head tube 50 that will receive a simply, or circular cuttop tube 52 and bottom tube 54, tubes of varying and exotic crosssectional profiles can be used easily, without the concern associatedwith filling gaps created by poorly cut weld surfaces, which oftenresult in non-circular cuts. Such an arrangement simplifiesmanufacturing in comparison to other methods for producing a reinforcedhead tube, which may require non-circular miter cuts in the top and downtubes. For example, in a head tube having an outer surface thereof ovalin shape to increase the wall thickness in the forward and rearwardsides, the miter cut in the top and down tubes preferably are also ovalin shape, which cannot be accomplished by a standard drilling operation.Instead, a more complex method must be used to create the miter cuts inthe top tube and down tube, which typically both increases costs andreduces accuracy. As described above, a precise fit between the outersurface of the head tube and the cut surfaces of the top and down tubesis highly beneficial in providing a strong welded joint.

In another embodiment of the present head tube 50, the outer surface ofthe back portion 82 defines a flat plane and frame tubes would beprovided with a flat mating surfaces to abut at right angles to the flatback portion 82 of the head tube 50.

With reference to FIGS. 7 and 8, additional features of the head tube 50are described. To further reduce weight, holes 100, 102 are provided inthe back side 82 of the head tube 50 because material inside of theinner profile of the top and down tubes 52, 54 is unnecessary.Preferably, the holes 100, 102 extend through the wall of the head tube50 and intersect the opening 70.

The holes 100, 102 may be of any suitable shape within the confines ofthe periphery of the top tube 52 and down tube 54, respectively. Inconventional head tubes, the weight reducing holes (comparable to holes100, 102) are circular in shape because circular holes are easier andcheaper to produce. However, to maximize the weight reduction, the holes100, 162 are preferably shaped and sized to approximate the innerprofile of the top tube 52 and the down tube 54 to enable the mostmaterial to be removed from the head tube 50. In order to obtain adesirable strength and stiffness to weight ratio, the top tube 52 anddown tube 54 may be manipulated, or shaped, into a non-circularcross-sectional shape.

Weight reducing holes that approximate the shape of such exoticallyshaped tubing are more difficult to produce than round holes in aconventional head tube. However, with the head tube 50 produced by apreferred process as described herein, the holes 100, 102 may be easily,and inexpensively, produced in a large variety of complex shapes tocorrespond with the shape of the top tube 52 and down tube 54. Becausedepressions (which later form the holes 100, 102) are initially producedby a forging die and/or ram, they may take on complex shapes without theadditional cost associated with producing complex shaped holes by astandard machining process. The depressions that form the holes 100, 102are created to a depth, from an outer surface of the head tube 50, suchthat the depression are intersected by the opening 70. Thus, thedepressions intersect with the opening 70 to create the holes 100, 102.Accordingly, the holes 100, 102 may assume complex shapes, but still bemanufactured in an efficient and relatively inexpensive manner incomparison to convention head tubes. A preferred process for creatingthe openings 100, 102 by a forging process is described in greaterdetail below with reference to FIGS. 10-13.

FIG. 9A is a cross-sectional view of the head tube 50 near the upperend, or upper reinforced portion 74, of the head tube 50. This viewillustrates the continuous curve of the weld surface 96 at this crosssection at the upper portion 74 of the head tube 50. In addition, theupper end 74 of the head tube 50 defines an average wall thickness. Afront portion 78 of the upper end 74 also defines an average wallthickness, generally forward of the steering axis As, and a back portion82 of the upper end 74 defines an average wall thickness, generallyrearward of the steering axis As.

FIG. 9B is a cross-sectional view of the head tube 50 at the middleportion 76. This view illustrates the continuous curve of the weldsurface 96 at the middle portion 76 of the head tube 50. The middleportion 76 also defines an average wall thickness. Furthermore, each ofthe front portion 78 and rear portion 82 define an average wallthickness.

FIG. 9C is a cross-sectional view of the head tube 50 near the lowerend, or lower reinforced portion 72. This view illustrates thecontinuous curve of the weld surface 96 at this cross section at thelower portion 72 of the head tube 50. The lower end 72 defines anaverage wall thickness and each of front and rear portions 78, 82 definean average wall thickness.

FIGS. 9A through 9C illustrate the varying wall thickness constructionof the head tube 50, as discussed in detail above. For example,comparing the average wall thicknesses of the head tube 50 in FIGS. 9Aand 9C with the wall thickness in FIG. 9B clearly illustrates thepreferred construction of a greater average wall thickness in the upperand lower portions 74, 72 of the head tube 50 in comparison to theaverage wall thickness of the middle portion 78. Such a constructionprovides increased strength and durability to the upper and lowerportions 74, 72 of the head tube 50, where stresses are higher, andreduces material in the middle portion 78 of the head tube, where thestresses are lower. In addition, preferably, the average wall thicknessof the lower portion 72 is greater than an average thickness of theupper portion 74, due to the higher stresses in the lower portion 72resulting from the added leverage of the front fork assembly 20, asdescribed in detail above.

Furthermore, FIG. 9C clearly illustrates the preferred variation in wallthickness within at least the lower portion 72 of the head tube 50,wherein the forward portion 84 has a greater average wall thickness thanthe rearward portion 86. As described above, the rearward portion 86receives support from the top tube 52 and down tube 54 in the assembledframe 14 and, therefore, may be provided with a lower wall thickness.Accordingly, the preferred head tube 50 advantageously optimizes bothstrength and weight. Similarly, the upper and middle portions 74, 76 mayhave a differing average wall thickness between the front portion 84 andthe back portion 86 to optimize the strength-to-weight ratio of theentire length of the head tube 50. In some instances, the front portion84 may have a lower average thickness than the back portion 86 withinthe upper and middle portions 74, 76 depending on the overall structureof the head tube 50, top tube 52 and down tube 54.

A preferred method for manufacturing a head tube 50 of complex shape andincluding complex shaped holes, is described with reference to FIGS.10-13. Step S1 involves providing a forging die. Preferably, a surfaceof the die comprises relieved features that are intended to be impressedon to the head tube 50 during the forging process. For example, thestructure that provides the reinforcement portions 72, 74 will berelieved into the die and will be impressed into a forging blank 120,shown in FIG. 11. Thus, the die preferably includes desired featuresreversed and relieved on the surface. The die is preferably made of amaterial that is harder than the material of the head tube 50, orforging blank 120, at the working temperatures during the forgingprocess. Because the die is of harder, features on the surface of thedie will be impressed into the softer blank 120.

Step S2 involves providing a forging ram. Preferably, a surface of theram comprises relieved features that are intended to be impressed on tothe head tube 50. For example, the structure that provides the complexshaped holes 100, 102 is relieved into the ram face and will beimpressed into the forging blank 120. Thus, the ram preferably includesthe desired features reversed and relieved on its surface. The ram ispreferably made of a material which is harder then the material of thehead tube 50, or forging blank 120, at the working temperatures duringthe forging process.

Step S3 involves forming the blank 120 that will be used in the forgingprocess. The blank 120 is desirably generally close to the mass of thefinal head tube 50 and, preferably, roughly the same mass as the finalhead tube plus the mass removed to form the opening 70. It will beappreciated that “roughly the same mass” includes a blank having greatermass than the final head tube 50 and creating excess material, or flash,between the die and ram. Thus, additional process steps may be includedto remove any flash from the blank 120, such as the use of a cuttingdie, machining or grinding, for example.

Preferably, however, the blank 120 is similar in dimension to thefinished head tube to reduce the force needed in the forging process.The blank 120 preferably is also roughly the same length as the finalhead tube 50. For example, if the finished head tube 50 is 6 inches inlength, the blank 120 should be formed to a similar length that accountsfor expansion lengthwise during the forging process. The blank 120 alsoshould be roughly the width and thickness of the final head tube. Forexample, if the head tube 50 is 2 inches thick and 3 inches wide, theblank 120 should be roughly the those dimensions, accounting for massdisplacement.

In one embodiment, a casting 120 (FIG. 11) is preferably used whichapproximates the finished shape of the head tube 50. In anotherembodiment, preferably bar stock of appropriate dimensions can be cut tothe approximate length of the final head tube 50 and used in theforging.

Step S4 involves forging the blank 120. A ram (preferably as describedabove) presses the blank 120 in to a die (preferably as described above)and forces the blank 120 material to conform to the shape of the die andram face resulting in a partially processed head tube 50, or work piece130 (FIG. 12). Both the die and the ram hold relieved features to forgeinto the blank 120. The die or ram can forge complex indentations intothe blank 120, such as the non-round indentations needed for producingcomplex shaped holes 100, 102 on the back side 82 of the head tube 50(FIGS. 7 and 8). After the forging process, the blank 120 preferably hasthe external dimensions of the finished head tube 50.

Step S5 involves creating the opening 70. An opening 70 is cut throughthe work piece 130 length wise (along the steering axis A_(S)) forreceiving the steer tube 66 of the front suspension fork 20. Anyfeatures forged into the work piece 130 with a depth great enough toextend into the volume of material removed by the creation of theopening 70 will produce an additional opening that intersects with theopening 70. For example, the weight reducing holes 100, 102 on the backside of the head tube 50 are preferably formed by the creation of theopening 70 intersecting the depressions corresponding to the holes 100,102 made by the forging process. Desirably, once the opening 70 iscreated, the work piece 130 is essentially in the final form of the headtube 50.

Although it is preferred that the process steps S1-S5 are performed inthe above-described order to produce a head tube 50, the process stepsmay be completed in an alternative order and still provide advantagesover conventional processes for producing head tubes. Furthermore, notall of the steps are necessarily required and additional process stepsmay be added. For example, as described above, if flash is present onthe blank, or work piece, additional process steps may be utilized toremove the flash. Other additional process steps may also be included,as will be appreciated by one of skill in the art.

With reference to FIGS. 14-20 the junction 200 formed by the head tube50, top tube 52 and bottom tube 54 is described in greater detail. FIG.14 is a flow chart of a preferred method for manufacturing a head tubejunction 200.

Step S100 involves providing a forging die (not shown). Preferably thedie comprises relieved features that are intended to be impressed on tothe head tube 50. For example, the structure that provides thereinforcement portions 72, 74 is relieved into the die and will beimpressed into a forging blank, such as the blank 120 of FIG. 11. Thedie contains the desired features reversed and relieved on the surface.The die is preferably made of a material which is harder then thematerial the head tube 50 is made of at the working temperatures duringthe forging process. Because the die is of harder material, features onits surface will be impressed into the softer material of the blank 120.

Step S110 involves providing a forging ram (not shown). Preferably, theram comprises relieved features that are intended to be impressed on tothe head tube 50. For example, the structure that provides the complexshaped holes 100, 102 is relieved into the ram face and will beimpressed into the forging blank 120. The ram contains the desiredfeatures reversed and relieved on its surface. The ram is preferablymade of a material which is harder than the material the head tube 50 atthe working temperatures of the forging process.

Step S120 involves forming the blank 120 used in a forging process toproduce the head tube 50. The blank 120 is preferably roughly the samemass as the final head tube 50 plus the mass removed to form the opening70. “Roughly” the same means the range of masses that will allow aforging process to form a bicycle head tube 50.

Preferably, the blank 120 is similar in dimension to the finished headtube 50 to reduce the force needed in the forging process. The blank 120preferably is roughly the same length as the final head tube 50. Forexample, if the finished head tube 50 is 6 inches in length, the blank120 should be formed to a similar length that accounts for expansionlength wise during the forging process. The blank 120 should be roughlythe width and thickness of the final head tube 50. For example, if thehead tube 50 is 2 inches thick and 3 inches wide, the blank 120 shouldbe roughly the those dimensions, accounting for mass displacement.

In one embodiment, preferably a casting 120 (FIG. 11) is used in theforging process. Desirably, the casting 120 approximates the finishedshape of the head tube 50. In another embodiment, preferably bar stockof appropriate dimensions can be cut to the approximate length of thehead tube 50 and used in the forging process.

Step S130 involves subjecting the blank 120 to a forging process. A ram(preferably as described above) presses the blank 120 into a die(preferably as described above) and forces the blank 120 materialconform to the shape of the die and ram face resulting in a partiallyfinished head tube 50, or work piece 130 (FIG. 12). Both the die and theram hold relieved features to forge into the blank 120. The die or ramcan forge complex indentations into the blank 120, such as thenon-circular indentations for producing the complex shaped holes 100,102 on the back side 82 of the head tube 50. After the forging process,the work piece 130 preferably has the external dimensions of thefinished head tube 50.

Step S140 involves creating the opening 70. An opening 70 is cut throughthe work piece length wise (along the steering axis A_(S)) for receivingthe steer tube 66 of a fork 20. Any features forged into the work piece130 with a depth great enough to extend into the volume of materialremoved by the creation of the opening 70 will produce an additionalopening intersecting the opening 70. For example, the weight reducingholes 100, 102 on the back side of the head tube 50 are formed by thevolume removed by the creation of the opening 70 intersecting thedepressions, corresponding to the holes 100, 102, formed during theforging process.

Step S150 involves providing frame tubing to form the top tube 52 anddown tube 54 to complete the head tube junction 200. Preferably theframe tubing is constructed of similar material to the head tube 50 toaid in the ease of attachment. For example, when welding two dissimilarkinds of metal the joint that is formed may not be of expected strength.If the metals are too dissimilar, they may not behave predictably or mixwhile in the liquid form, and may combine with undesirablecharacteristics. Alternatively, an additional component, such as a lug,that is capable of being joined to the head tube 50 by welding may beused to connect dissimilar frame material to the head tube 50.

Step S160 involves cutting a recess R (the hatched area illustrated inFIG. 18A) into the planar end of the frame tubes, or “mitering” theframe tubes. As described above the head tube 50, in one embodiment,preferably has an extension of a constant radius. A constant radius ofthe surface 96 created by the extension of the head tube 50 allows theuse of simple, circular cuts in the mating portions of the frame tubes.In Step S160 of this embodiment, simple radial cuts are cut into themating ends of the top and down tube 52, 54.

Step S170 involves attaching the head tube 50 to the top tube 52 anddown tube 54. Preferably, when working with aluminum tubing a weld isused for joining. By providing a head tube 50 defining an attachmentsurface 96 having a constant radius and frame tubes (top tube 52 anddown tube 54) cut with a corresponding radius recess at the mating ends,the welding process will produce strong, consistent welds, with littlegap filling required. Furthermore, such a method allows for theproduction of a complex shaped head tube 50. Accordingly, the shape ofthe head tube 50 may be designed, at least in part, in an effort to heatdistribution during the welding of the top tube 52 and down tube 54 tothe head tube 50, such as by manipulating the amount of materialprovided near the welding zones of the head tube 50, as will beappreciated by one of skill in the art.

Although it is preferred that the process steps S100-S170 are performedin the above-described order to produce a head tube junction 200, theprocess steps may be completed in an alternative order and still provideadvantages over conventional processes for producing head tubes.Furthermore, not all of the steps are necessarily required andadditional process steps may be added.

FIG. 16 illustrates a cross-section of the head tube 50, down tube 54and top tube 52 joined with the above method to form a head tubejunction 200. This figure illustrates the bottom tube 54 being attachedto the back side 82 of head tube 50 at the weld surface 96. The top tube52 is also secured to the upper most weld surface 96. Desirably, each ofthe top and down tubes 52, 54 are joined to the head tube 50 by a weldedbead along substantially the entire periphery of the tubes 52, 54 andcorresponding areas of the surface 96 defining the periphery of theholes 100, 102, as shown in FIG. 17. However, in some instances, facingor overlapping surfaces of the top tube 52 and down tube 54 may bewelded to one another, rather than to the head tube 50. Such anarrangement may be used on smaller frame sizes due to a limitation onthe desirable length of the head tube 50, which is less than thecombined vertical dimensions of the top and down tube 52, 54.

FIGS. 18A, 18B and 18C are cross-sectional views taken along the upperend, middle and lower end of the junction 200, respectively. The FIGS.18A, 18B and 18C generally correspond with the cross-section views ofthe head tube 50 of FIGS. 9A, 9B and 9C, respectively, except that thetubes 52 or 54, as appropriate, are shown. FIGS. 18A and 18C illustratethe junction between the head tube 50 and the top tube 52 and down tube54, respectively.

Although the present invention has been disclosed in the context ofseveral preferred embodiments, it will be understood by those of skilledin the art that the scope of the present invention extends toalternative embodiments and/or uses of the invention and obviousmodifications and equivalents thereof. For example, certain features ofthe disclosed head tube 50 may be utilized alone, without theadditionally disclosed features. In one contemplated arrangement, a headtube is provided having a varying wall thickness between forward andrearward portions thereof. In another contemplated arrangement, a headtube is provided having an enlarged, constant radius attachment surface.Accordingly, the invention is not intended to be limited to thespecifically disclosed embodiments, but is intended to be defined solelyby the appended claims.

1. A bicycle, comprising: a front wheel; a rear wheel; a frame assemblycomprising a main frame and a sub-frame movable relative to said mainframe and configured to carry said rear wheel; a shock absorberextending between and connected to said main frame and said sub-frame;wherein said main frame comprises a down tube and a monolithic bottombracket support, said monolithic bottom bracket support connected to arearward end of said down tube and including an opening configured tosupport a pedal crank assembly, said monolithic bottom bracket supportsurrounding a portion of said shock absorber.
 2. The bicycle of claim 1,wherein said monolithic bottom bracket support comprises an open trussconfiguration.
 3. The bicycle of claim 1, wherein said monolithic bottombracket support comprises a first mount portion configured to supportsaid sub-frame and a second mount portion configured to support saidshock absorber.
 4. The bicycle of claim 1, wherein said monolithicbottom bracket support is manufactured by a process including a forgingstep.
 5. The bicycle of claim 1, wherein said monolithic bottom bracketsupport fully encircles said shock absorber.
 6. A bicycle, comprising: afront wheel; a rear wheel; a frame assembly comprising a main frame anda sub-frame movable relative to said main frame and configured to carrysaid rear wheel, said main frame comprising a forged bottom bracketsupport defining an opening configured to support a pedal crank assemblyfor rotation about a crank axis, said main frame further comprising adown tube including a substantially linear intermediate section defininga down tube axis, wherein said down tube axis extends below said crankaxis; and a shock absorber connected to and extending between said mainframe and said sub-frame, said shock absorber connected to said mainframe for rotation about a pivot axis positioned forward of said openingof said bottom bracket support.
 7. The bicycle of claim 6, wherein saidpivot axis is defined by said forged bottom bracket support.
 8. Thebicycle of claim 6, wherein said sub-frame comprises a multiple linkageassembly.
 9. The bicycle of claim 8, wherein said sub-frame comprises apair of chain stays, a pair of seat stays and a link.
 10. The bicycle ofclaim 9, wherein said seat stays are rotatably coupled to said chainstays.
 11. The bicycle of claim 10, wherein said rear wheel is carriedby said seat stays.
 12. A bicycle, comprising: a front wheel; a rearwheel; a frame assembly comprising a main frame and a sub-frame movablerelative to said main frame and configured to carry said rear wheel,said main frame comprising a head tube, a down tube and a forged bottombracket support defining an opening configured to support a pedal crankassembly for rotation about a crank axis, said down tube connected toand extending between said head tube and said bottom bracket support;and a shock absorber connected to said main frame at a first locationfor rotation about a first pivot axis and connected to said sub-frame ata second location, said first pivot axis positioned forward of a linepassing through said crank axis and a center point of said down tube atthe junction of said down tube and said head tube.
 13. The bicycle ofclaim 12, wherein said pivot axis is defined by said forged bottombracket support.
 14. The bicycle of claim 12, wherein said sub-framecomprises a multiple linkage assembly.
 15. The bicycle of claim 14,wherein said sub-frame comprises a pair of chain stays, a pair of seatstays and a link.
 16. The bicycle of claim 15, wherein said seat staysare rotatably coupled to said chain stays.
 17. The bicycle of claim 16,wherein said rear wheel is carried by said seat stays.